Many diseases influence displacement, deformation, and mechanics indices, such as strain, twist, and torsion, of the tissue or organ compared to the normal status. Quantitative assessment of these biomarker parameters indices is of growing interest and importance. For example, quantitative imaging of myocardial motion and strain in the cardiovascular system is an emerging field as it helps to understand and measure the complex moving and contraction patterns of the heart and vessels can be helpful in both research and clinical settings.
In addition to conventional applications, such as ischemia detection and evaluation of myocardial mechanics related to cardiac surgery, newer applications include quantifying mechanical dyssynchrony in heart failure and measuring the functional effects of experimental therapies such as stem cell infusion. Other clinical applications include evaluation of brain motion, characterization of skeletal muscle contraction, and assessment of vessel wall deformation and stretching. Therefore, the rapid and accurate evaluation of displacement and subsequent deformation and mechanics indices in tissue is of great clinical interest.
Magnetic resonance imaging (MRI) has been used for this purpose. Displacement Encoding with Stimulated Echoes (DENSE) is an MRI technique for quantitative imaging of tissue motion. This technique encodes tissue displacement into the phase of the magnetic resonance (MR) signal. Displacement or motion values can be extracted from the MR phase images for each displacement encoded direction, and combined to generate a displacement map. The displacement values can be further used to calculate the deformation and mechanics indices including but not limited to strain, twist, and torsion.
The DENSE technique that is three-dimensional (3D) both with respect to spatial coverage and motion measurement is beneficial for a complete assessment of tissue motion, especially for organs with complex movement or deformation patterns, such as the heart. However, 3D acquisition usually requires a prolonged scan time that is not preferable and/or not feasible in the clinical environment. Due to this scan time consideration, quantitative two-dimensional (2D) DENSE imaging is more common than 3D DENSE imaging. However, there is a trade-off in using 2D DENSE imaging—lack of volumetric spatial coverage of the organ. Alternatively, 2D DENSE imaging can be performed in multiple slice locations, one slice at a time, to provide the desired spatial coverage, but again at the cost of scan time.
A simultaneous multi-slice 2D imaging technique is capable of acquiring data from multiple slices with no or minimal penalty of scan time compared to a single slice 2D imaging method. In conventional 2D imaging in MRI, multiple slices are acquired sequentially or in an interleaved manner. In the simultaneous, multiband approach, multiple slices are acquired simultaneously and thereby the acquisition is accelerated. Simultaneous acquisition of multiple slices is achieved through specially-designed RF excitation pulses, as well as related image reconstruction methods.
This document describes a comprehensive approach to provide a 2D multi-slice quantitative assessment of displacement, deformation, and mechanics indices of tissue or organ by combining the DENSE technique and the multiband technique, with the scan time equivalent to the short scan time of the conventional single slice 2D imaging while providing spatial volumetric coverage similar to the 3D imaging.